The interruption of normal power supply can be caused by a variety of reasons, for example, earthquake, flood damage, adverse weather conditions, or utility unreliability. In the event that a normal power source, such as an electric utility, experiences an outage and fails, it is often necessary to supply critical and essential electrical needs by means of a standby electrical power system.
Often, the standby power supply system is an on-site electrical power source suitable to the needs of the applicable legal requirements and user criteria. The standby or emergency power supply system functions to provide a source of electrical power of required capacity, reliability and quality within a specified time after loss or failure of the normal power supply. The emergency power supply system varies depending upon the particular situation, for example, there may be a specified maximum time for which the load terminals of the transfer switch are permitted to be without acceptable electrical power. Quick transfer is especially important where critical equipment is involved, as in hospitals, airports and computer installations.
With conventional transfer switches, it is possible for the load to be transferred to the standby power source before the standby power source has built up enough energy to sufficiently handle the load. To address this problem, a suitable timer mechanism must be employed to delay the transfer, or a capacitor must be employed to supply the necessary power at the outset after transfer.
One type of conventional transfer switch utilizes a linear actuator mechanism which has a single central solenoid with a plunger which can be ejected from either end. On each side of the solenoid are two separate contact blocks. With this design, a bidirectional linear induction motor is utilized. As mentioned above, one or more boosters or motor-starting capacitors are required. In order to prevent the application of power to the load from both sources at the same time, this linear actuator mechanism also has a mechanical interlocking beam.
However, conventional actuator mechanisms such as the one described require a substantial amount of space, thereby making the unit unsuitable for some applications and more costly. Further, the linear motor utilized with the conventional transfer switch is relatively expensive and requires additional space.
In addition, it is possible for the interlocking beam to become displaced, for example, if a screw becomes loose. In that event, power could be applied from both the primary power source and the standby power source, which could result in dangerous short circuits and destruction of the standby system.
The present invention addresses these and many other problems associated with currently available transfer switches.